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.\"     @(#)vis.1	8.4 (Berkeley) 4/19/94
.\" $FreeBSD: src/usr.bin/vis/vis.1,v 1.12 2005/02/13 22:25:25 ru Exp $
.\"
.Dd June 25, 2004
.Dt VIS 1
.Os
.Sh NAME
.Nm vis
.Nd display non-printable characters in a visual format
.Sh SYNOPSIS
.Nm
.Op Fl cbflnostw
.Op Fl F Ar foldwidth
.Op Ar
.Sh DESCRIPTION
The
.Nm
utility is a filter for converting non-printable characters
into a visual representation.
It differs from
.Ql cat -v
in that
the form is unique and invertible.
By default, all non-graphic
characters except space, tab, and newline are encoded.
A detailed description of the
various visual formats is given in
.Xr vis 3 .
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl b
Turns off prepending of backslash before up-arrow control sequences
and meta characters, and disables the doubling of backslashes.
This
produces output which is neither invertible or precise, but does
represent a minimum of change to the input.
It is similar to
.Dq Li cat -v .
.It Fl c
Request a format which displays a small subset of the
non-printable characters using C-style backslash sequences.
.It Fl F
Causes
.Nm
to fold output lines to foldwidth columns (default 80), like
.Xr fold 1 ,
except
that a hidden newline sequence is used, (which is removed
when inverting the file back to its original form with
.Xr unvis 1 ) .
If the last character in the encoded file does not end in a newline,
a hidden newline sequence is appended to the output.
This makes
the output usable with various editors and other utilities which
typically do not work with partial lines.
.It Fl f
Same as
.Fl F .
.It Fl l
Mark newlines with the visible sequence
.Ql \e$ ,
followed by the newline.
.It Fl n
Turns off any encoding, except for the fact that backslashes are
still doubled and hidden newline sequences inserted if
.Fl f
or
.Fl F
is selected.
When combined with the
.Fl f
flag,
.Nm
becomes like
an invertible version of the
.Xr fold 1
utility.
That is, the output
can be unfolded by running the output through
.Xr unvis 1 .
.It Fl o
Request a format which displays non-printable characters as
an octal number, \eddd.
.It Fl s
Only characters considered unsafe to send to a terminal are encoded.
This flag allows backspace, bell, and carriage return in addition
to the default space, tab and newline.
.It Fl t
Tabs are also encoded.
.It Fl w
White space (space-tab-newline) is also encoded.
.El
.Sh SEE ALSO
.Xr unvis 1 ,
.Xr vis 3
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.4 .
.Sh BUGS
Due to limitations in the underlying
.Xr vis 3
function, the
.Nm
utility
does not recognize multibyte characters, and thus may consider them to be
non-printable when they are in fact printable (and vice versa).
